I doubt that you could make one from scratch for $50. You would be better off saving money until you have enough to buy one. You need a Stainless steel pot for where the water boils, and an after filter made from charcoal.
Here's a link for the one I bought. It's $190.00 here, but some charge $299 for the same model (4000 model). It makes a gal every 4 hours which is more than I by myself can use or drink. It shuts off automatically so you don't have to be there while it works.
Here's the link. There is 2 links that show diagrams of how they work. One at the top of the page "How steam distillation works" and about 1/3 of the way down the page under the 4000 distiller (my model), "Steam distillation diagram".